Throughout the United States, there are many underpass structures that define a tunnel extending under a roadway, such as, for example, a culvert or pipe arch formed of corrugated sheet metal or other material which can change in shape or cross-sectional configuration over a period of time. Frequently, it is desirable to determine the degree of change in configuration or shape by comparing a current actual cross-sectional shape with the original or a prior cross-sectional shape to insure that the structure continues to have sufficient strength to support the load above the structure. While horizontal and vertical measurements are sometimes manually made of the structure at intervals along the length of the tunnel, such measurements require substantial time and effort, resulting in significant cost. There are also various forms or types of complex laser equipment for measuring and/or detecting the inner surfaces of a bore or pipe, such as disclosed, for example, in U.S. Pat. Nos. 7,164,476, 7,345,757, 7,349,083,7,557,914 and 7,567,350. However, none of the equipment is suitable for quickly, economically and efficiently measuring and determining the cross-sectional shape or configuration of a tunnel defining structure.